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Using BOSS (Baryon Oscillation Spectroscopic Survey), a component of the third Sloan Digital Sky Survey from the Lawrence Berkeley National Laboratory in California, scientists have produced the most accurate measurements of when dark energy arose and caused the universe to accelerate its expansion.
Martin White, of Berkeley Lab’s Physics Division states in the press release, “BOSS’s first major cosmological results establish the accurate three-dimensional positions of 327,349 massive galaxies across 3,275 square degrees of the sky, reaching as far back as redshift 0.7 – the largest sample of the universe ever surveyed at this high density.” White is a professor of physics and astronomy at the University of California at Berkeley, and chair of the BOSS science survey teams.
The notion that the universe is expanding came about in the 1920s, when American astronomer Edwin Hubble discovered that all of the galaxies whose light shift he measured had produced a red shift– they were moving away from the Earth. The universe is continuously accelerating in its expansion.
Accelerated expansion was announced only fourteen years ago. Astronomers believe that a mysterious force called dark energy is the cause of this accelerated expansion, which is believed to have first occurred seven billion years ago. Presently, dark energy makes up nearly 75% of the universe’s total mass and energy.
Since the proposal of dark energy, the idea of it and when it came about precisely remained elusive. But just last week, the group of scientists at Berkley created the most precise map of dark energy, which looks billions of years into the past.
In order to create a map of dark energy, and to determine when dark energy caused the universe to suddenly accelerate expansion, the team of scientists working with BOSS produced precise measurements of the distances between each of the hundreds of thousands of galaxies, while also analyzing the galaxies’ red shifts, which allowed them to calculate the rate of expansion. To determine the distances, BOSS used a technique known as baryon acoustic oscillation.
Baryon acoustic oscillation occurs when baryons (i.e. “ordinary” matter) cluster due to the pressure of sound waves that moved through the universe when the universe was still very young (not even 400,000 years old) and hot and having varied densities because of the mixture of light and matter.
The universe has not always been expanding; rather, the expansion has been slowing down due to the pull of gravity the universe placed on itself. While BOSS was creating the map, it was able to pinpoint when exactly dark energy suddenly “turned on,” and accelerated expansion: six billion years after the universe came into existence.
The map may produce insight into dark energy and what its nature is, and it can also help astronomers understand the structure of the universe, and its expansion rate.
“For the past 13 years, we’ve had a simple model of how dark energy works,” David Schlegel of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory in California, BOSS’ principal investigator tells Space.com. “But the truth is, we only have a little bit of data, and we’re just beginning to explore the times when dark energy turned on. If there are surprises lurking out there, we expect to find them.”
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